But it frequently happens that the fibrinous element of the blood, though incrmsed in quantity, does not possess its normal plasticity ; and the deposits which are the consequence of its effusion are far from being as organizable as in the preceding case, and are either im perfectly organizable, or caco-plastic, or alto gether unorganizable or aplastie. The tendency to such deposits may arise from various causes. Thus, when the inflammation is from the firSt of a low or asthenic character, or when the blood is previously in an unhealthy condition (as, for instance, when there is a deficiency in the number of red particles, the presence of the normal amount of which seems important to the complete elaboration of the fibrin), no other kind of deposit takes place from the first ; and even when organizable plasrna has been co piously thrown out in the first instance, it is not unfrequently succeeded by caco-plastic, or aplastic products,—either from a change in the character of the inflammatory process itself,—or because the late products are thrown out in such a position as to be cut off from that influ ence of living surfaces around, which is neces sary to their coniplete organization. Between the organizable or euplastk, and the eaco-plastic, and aplastic deposits, the gradations are almost insensible. The cells and fibres which are characteristic of the first diminish in number and are less perfectly formed; and they are replaced by a granular a.morphous matter, which possesses but little cohesion, and which, being totally incapable of entering into any form of tissue, acts as a foreign body, and becomes a source of irritation. The limited space allotted to this subject prevents any more particular description of these products from being here given ; but there is one which must not be overlooked, since its occurrence is very fre quent, its effects upon the system most im portant, and its character very peculiar. The product alluded to is pus. This is characterized by the preience of a number of cells of a pe culiar aspect, having a very tuberculated or mulberry surface, which are seen floating in a fluid, termed liquor puris, which is of an albu minous or low fibrinous character, being entirely destitute of organizability. Now the production of pus in an inflamed part, or in other words, the act of suppuration, may be due to one of three causes, viz.,—the intensity of the inflammation ; the presence of air, which becomes a source of irritation ; and a previously vitiated state of the blood. Various attempts have been made to show that the pus-globule is a degenerated red or white corpuscle of the blood ; but it seems more probable, however, that it does not escape from the vessels as a complete cell, but as a cell-germ, which may have had its origin in a white corpuscle of the blood ; and which, under favourable circum stances, might have produced an exudation corpuscle. At any rate, it must be regarded as a degenerated form of cell ; and the liquor puris must be considered as analogous to the plasma of the blood in a degenerated state" In what manner the inflammatory process determines the formation of the pus cell, and the consequent degradation of the product, we are at present unable to state ; but that the degree of irritation in the part has an influence upon it is 'evident from the effects of the contact of air upon inflamed surfaces, causing those elements to take the form of pus, which would otherwise have been thrown out as a plastic deposit. This circumstance would seem to indicate, beyond all doubt, that the exudation and pus-corpuscles, the plastic lymph, and the aplastic liquor puris have the same origin, but that their character is determined by local cir cumstances. There is great reason to believe, that when pus is introduced into the blood, it may induce such a change in the character of the fluid, as speedily to impair its vital proper ties ; so that the pus-corpuscles will rapidly propagate themselves in the blood, and the plasticity of the liquor sanguinis will be dimi nished. In this manner the whole system will be seriously affected, and there will be a tend ency to deposits of pus in various organs— especially those which, like the lungs and liver, serve as emunctories to the system—without any previous inflammatory changes in these parts.
The last form of disordered nutrition which we shall consider is that which takes place in the tuberculous diathesis, and which is marked by the deposition of tubercular matter, in place of the normal elements of tissue, both in the ordinary process of nutrition, and still more when inflammation is set up. From an exami
nation of the blood of tuberculous subjects it appears that the fibrinous element is not defi cient in amount, but that it is not duly elaborated, so that the coagulum is loose, and the red cor puscles are found to bear an abnormally low proportion to it. We can understand, therefore, that such a constant deficiency in plasticity, must affect the ordinary nutritive process; and I that there will be a liability to the deposit ofl caco-plastic products, without inflammation, instead of the normal elements of tissue. Such appears to be the history of the formation tubercles in the lungs and other organs, whe it occurs as a kind of metamorphosis of th ordinary nutritive process; and in this mann it may proceed insidiously for a long period, that a large part of the tissue of the lungs sh be replaced by an amorphous deposit, witho any other ostensible sign than an increasii difficulty of respiration. It is in the different forms of tubercular deposit that we see the gradation most strikingly displayed between the euplastic and the aplastic formations. In the semi-transparent, miliary, grey, and tough yel low forms of tubercle, we find traces of organi zation in the form of cells and fibres, more or less obvious; these being sometimes almost as perfectly formed as those of plastic lymph, at least on the superficial part of the deposit, which is in immediate relation with the living structures around, and sometimes so degen erated as scarcely to be distinguishable. In no instances do such deposits ever undergo further organization, and therefore they must be re garded as eaeo-plastic. But in the opaque, crude, or yellow tubercle, we do not find even these traces of definite structure; for the matter of which it consists is altogether granular, more resembling that which we find in an albuminous coagulum. The larger the proportion of this kind of matter in a tubercular deposit, the more is it prone to soften, whilst the semi-organized tubercle has more tendency to contraction.
affected with chronic tubercular deposits, by an impairment of the process of textural nutrition ; for these deposits, acting like foreign bodies, may of themselves become sources of irritation ; and the perversion of the-structure and func tions of the part renders it peculiarly suscep tible of the influence of external morbific causes. These views, at which several recent physiologists and pathologists have arrived on independent grounds, seem to reconcile or supersede all the discordant opinions which have been upheld at different times regarding the nature of tubercle, and lead to the soundest views with respect to the treatrnent of the diathesis.
Parasitic growths.—Besides the products of disordered nutrition, which have been just considered, there is another class of morbid structures, differing from the preceding in well marked and important characters. Their exist ence and mode of growth cannot generally be traced to simple variations in the local circula tion and in the formative powers of the parts affected ; and they enjoy an independent vitality, which causes their maintenance and increase to be influenced but little by the state of the textures around, except so far as this may affect the supply of blood which they receive. They bear a certain resemblance to other tis sues, in an early stage of the developement of the latter ; being for the most part composed of cells and fibres, combined in different modes.: and they also correspond with them in chemical constitution. It is by this last character, in deed, that they are to be distinguished from the vegetable organisms, which are unquestionably developed occasionally in the living animal body, and which often closely resemble them in aspect. The best practical division of parasitic growths is into the non-malignant and the malignant ;—the former being of local origin, not tending to reappear in distant parts of the body, and having no injurious effect upon the surrounding tissues, except by the pressure they may exercise upon them, or the nourishment they may withdraw ;—whilst the latter, having once made their appearance in thebody, tend to reappear at distant parts (even after the original growth has been removed), induce a complete change of structure and of actions in the organs in which they are de veloped, and exert a very depressing influence upon the bodily system at large.